Film stress management for MEMS through selective relaxation

ABSTRACT

An apparatus comprising a microelectromechanical system. The microelectromechanical system includes a crystalline structural element having dislocations therein. For at least about 60 percent of adjacent pairs of the dislocations, direction vectors of the dislocations form acute angles of less than about 45 degrees.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 11/968,399filed on Jan. 2, 2008, now U.S. Pat. No. 8,138,495 to George Watson,entitled “FILM STRESS MANAGEMENT FOR MEMS THROUGH SELECTIVE RELAXATION,”currently allowed; commonly assigned with the present invention andincorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present disclosure is directed, in general, to an apparatus thatcomprises a microelectromechanical system (MEMS) and method ofmanufacture thereof.

BACKGROUND OF THE INVENTION

MEMS can include parts (structural elements) that are above, below or inthe plane of a substrate, to form three-dimensional features. The MEMS'sstructural elements, in their final form, can be configured to bestraight or bent. To improve the yield and performance of the MEMS, itis desirable to be able to form such MEMS structural elements intoreproducible shapes. For instance, it is sometimes desirable for a MEMSmanufacturing process to form batches of MEMS having bent structuralelements that are all bent in the same position and to the same degree,or, having straight elements that all have the same extent ofstraightness. To obtain reproducible performance, it is also sometimesdesirable for bent structural elements to remain bent and for straightelements to remain straight throughout the operational lifetime of theMEMS.

SUMMARY OF THE INVENTION

One embodiment is an apparatus comprising a microelectromechanicalsystem. The microelectromechanical system includes a crystallinestructural element having dislocations therein. For at least about 60percent of adjacent pairs of the dislocations, direction vectors of thedislocations form acute angles of less than about 45 degrees

Another embodiment is a method of manufacturing an apparatus thatcomprises forming a microelectromechanical system having a crystallinestructural element. Forming the microelectromechanical system includesproviding a substrate having a first crystal layer located thereon andpatterning the first crystal layer to form a lattice dislocationblocking feature. One or more nucleation sites are formed in theblocking feature. Forming the microelectromechanical system alsoincludes forming one or more nucleation sites in the lattice dislocationblocking feature, and covering the first crystal layer with a secondcrystal layer. The first crystal layer and the second crystal layer havebulk lattice constants that differ by at least 0.1 percent. Misfitdislocations form at an interface between the first crystal layer andthe second crystal layer. At least about 60 percent of adjacent pairs ofthe misfit dislocations have direction vectors that form acute angles ofless than about 45 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the disclosure are best understood from the followingdetailed description, when read with the accompanying FIGUREs.Corresponding or like numbers or characters indicate corresponding orlike structures. Various features may not be drawn to scale and may bearbitrarily increased or reduced in size for clarity of discussion.Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 presents a perspective view of a portion of an example apparatushaving a MEMS therein;

FIG. 2 presents a perspective view of a portion of a second exampleapparatus and having a MEMS therein;

FIG. 2A presents a plan of a portion of the second example apparatus;

FIG. 3 presents a perspective view of a portion of a third exampleapparatus having a MEMS therein;

FIG. 4 presents a perspective view of a portion of a fourth exampleapparatus having a MEMS therein;

FIGS. 5-10B present perspective views of selected steps in an examplemethod of manufacturing an apparatus, e.g., as in FIGS. 1-4; and

FIGS. 11-13 present perspective views of selected steps in a secondexample method of manufacturing an apparatus, e.g., as in FIGS. 1-4.

DETAILED DESCRIPTION

The present disclosure benefits from the recognition that the yield andperformance of MEMS structures can be worsened by the presence ofnaturally occurring line defects, called dislocations. In the MEMSmanufacturing industry, line defects are generally considered to beundesirable because such defects can cause the malfunction of the MEMS.For instance, misfit dislocations can form randomly at the interfacebetween strained structural elements of the MEMS. Such misfitdislocations can cause random and non-uniform stress relaxation of thestructural elements, which in turn, can cause random and non-uniformchanges in the shape of the structural element from one MEMS to the nextMEMS in a batch fabrication process. For these reasons, steps are oftentaken to prevent or reduce the formation of line defects in thestructural elements of MEMS structures.

This is in contrast to the present disclosure, which recognizes that theintentional and controlled promotion of line defects (for example,misfit or edge dislocations) can be used to control strain formation andrelaxation in MEMS structural elements. Indeed, the present disclosurerecognizes that the combination of selective relaxation processes, suchas defect nucleation and dislocation blocking, are new result-effectivevariables for controlling the shape and/or stiffness of the structuralelements.

One embodiment is an apparatus that comprises a MEMS. FIG. 1 shows aperspective view of an example apparatus 100 and a portion of a MEMS102. In some embodiments, the apparatus 100 is configured as anoptoelectronic component, such as a receiver or transmitter apparatusthat implements adaptive optics or spatial light modulation. The MEMScan have linear dimensions in a sub-micron to millimeter-sized range andcan perform mechanical, electrical, fluidic, optical, acoustic,magnetic, or other functions well know to those skilled in the art.Example configurations of the MEMS 102 include a mirror, a spring, or astructural support member.

The MEMS 102 includes a crystalline structural element 105. Thecrystalline structural element 105 can be a component that moves duringthe MEMS's 102 normal operation, or a non-moving component. As shown inFIG. 1, the crystalline structural element 105 is located on a substrate107. The crystalline structural element 105 has dislocations 110therein. The crystalline structural element 105 is composed of a singlecrystal layer or a plurality of single crystal layers. Amorphous orpolycrystalline materials are not preferred because the stresses in suchmaterials are hard to control or maintain throughout various processsteps to form a structural element into its pre-designed final shape.

The term dislocation 110 as used herein refers to substantially lineardefects that are located at the interface between two strained crystallayers. The dislocation can be an edge dislocation or a misfitdislocation. Edge dislocations refer to a discontinuity in the otherwiseideal stacking of atoms in a crystal (e.g., a step). Misfit dislocationsoriginate due to a difference (for example, an at least about 0.1%difference) in the lattice constants of the two crystal layers. A misfitdislocation can be an isolated row of broken bonds along the interfacebetween two such layers. The row of broken bonds could be reconstructed,with the misfit dislocation comprising two partial dislocations and astacking fault, or in some cases, a hollow tube. Two or more misfitdislocations originating at the interface between two crystal layers caninitiate the formation of an edge dislocation that penetrates andextends in to one of the crystal layers.

Misfit and edge dislocations can be identified and quantified byinspecting plan or cross-sectional views of transmission electronmicroscope (TEM) scanning or cathodoluminescence (CL) images of crystallayers. Typically, individual misfit or edge dislocations appear asvisible lines in CL images of crystals. Examples of such visualizationsare presented in E. A. Fitzgerald, G. P. Watson, R. E. Proano, D. G.Ast, P. D. Kirchner, G. D. Pettit, and J. M. Woodall, “Nucleationmechanisms and the elimination of misfit dislocations at mismatchedinterfaces by a reduction of growth area”, J. Appl. Phys., 65:2220(1989), which is incorporated by reference herein in its entirety.

A substantial majority (for example, at least about 60 percent, morepreferably, for at least about 80 percent, and even more preferably atleast about 90 percent) of the dislocations 110 are substantiallyparallel to each other. For instance, for the majority of dislocations110, direction vectors 115 for adjacent pairs of dislocations 110 forman acute angle 120 of less than about 45 degrees. More preferably theangle 120 is less than about 20 percent and even more preferably lessthan about 10 percent. In some embodiments, at least about 80 percent ofthe adjacent pairs of the dislocations 110 form acute angles 120 of lessthan about 20 degrees. The term direction vector 115, as used herein,refers to a magnitude-free vector that indicates the direction ofpropagation of a dislocation 110. The direction of propagation or growthof the dislocation 110 is signified by its direction vector 115. Byconvention, the direction vectors 115 are taken to form angles 120 of 90degrees or less herein so that inversion of one of the corresponding twodirection vectors 115 does not change the angle 120 between the twodirection vectors 115.

FIG. 1 shows an example determination the acute angle 120 between thedirection vectors 115 for a pair of dislocations 110. The exampledislocations are designated as first and second dislocations 122, 123.The acute angle 120 is determined for the two adjacent dislocations 122,123 with their respective direction vectors 125, 126 placed at the sameorigin. It will be apparent to one skilled in the art that twodislocations 110 that are parallel to each other will have an acuteangle 120 of about zero, while two dislocations 110 that areperpendicular to each other have an acute angle 120 of 90 degrees.

The direction of propagation of the dislocations 110 can be controlledby the predefined selection of locations to form defect nucleation sites130 in the crystalline structural element 105. The direction ofpropagation of the dislocations 110 can be further controlled byblocking the growth of dislocations 110 in undesired directions usinglattice dislocation blocking feature 135. A lattice dislocation blockingfeature can be a raised or lowered portion of the substrate 107 that isshaped to have an abrupt structural transition above or below the planeof the substrate 107. For instance, the blocking feature can be mesa (araised feature) or a trench (a lowered feature) having at least onesurface that forms an about 90° or −90° angle with respect to the planeof a substrate. Dislocation growth is controlled such that the majorityof dislocations, originating from the nucleation sites 130, aresubstantially parallel to each other, while the blocking features 135can deter the growth of dislocations 110 in undesired directions.

In some cases, the crystalline structural element 105 includes atomsimplanted at nucleation sites 130 of the dislocations 110. The implantedatoms cause local disruptions or damage to the lattice structure of thecrystalline structural element 105, which in turn, can promote theformation of dislocations 110. In other cases, the nucleation sites canbe formed by other means of creating local disruptions or damage to thecrystal lattice structure. Examples include micro- or nano-indentationprocesses.

In some cases, such as shown in FIG. 1, the crystalline structuralelement 105 itself can be the blocking feature 135. As shown in FIG. 1,the crystalline structural element 105 is a blocking feature 135, inparticular a raised feature, located above a plane 140 of the substrate107, such that there is an abrupt transition from the substrate 107 tothe crystalline structural element 105. A surface 142 of the elementforms an angle 144 of about 90° with respect to the substrate's topplane 140. Configuring the crystalline structural element 105 as ablocking feature 135 helps to deter to propagation of the dislocationsinto the substrate 107 or into non-raised portions of the element 105.

For the embodiment depicted in FIG. 1, the crystalline structuralelement 105 includes two adjacent single crystal layers 150, 152. Bothof the crystal layers 150, 152 can be part of the blocking feature 135.The two crystal layers 150, 152 have different bulk lattice constants.The term bulk lattice constant, as used herein, refers to the latticeconstant of a single crystal in the absence of the stress relaxationmethods described herein. In some cases the bulk lattice constant can bethe asymptotic value of a lattice constant of a single crystal far awayfrom interfaces with other materials. For the embodiment depicted inFIG. 1, the dislocations 110 are misfit dislocations located at aninterface 155 between the crystal layers 150, 152.

The crystal layers 150, 152 have substantially different bulk latticeconstants. For example, bulk lattice constants can differ by more thanabout 0.1 percent. In some preferred embodiments, the crystal layers150, 152 have bulk lattice constants that differ by about 0.1 to 2percent. In some embodiments, one of the crystal layers 150, 152 is madeof silicon and the other of the crystal layers 150, 152 is made ofsilicon germanium. For crystal layers 150, 152 having bulk latticeconstants that differ by less than about 0.1 percent, there may beinsufficient strain to cause the formation of misfit dislocations 110.For crystal layers 150, 152 having bulk lattice constants that differ bymore than about 4 percent, there may be so much strain that excessivenumbers of random misfit dislocations 110 are formed throughout theelement 105.

As noted above, the location, number, and propagation direction of thedislocations 110 in the crystalline structural element 105 provides anew set of result-effective variables for controlling the final shape ofthe element 105. The final shape of the element 105 is adopted when theelement 105 is partially released from a substrate 107. For instance, arelease process (e.g., a material etch process) that frees part 160 ofthe element 105 from the substrate can result in a change in theelement's 105 shape, as a means reduce residual stresses in the element105. As shown in FIG. 1, a part 165 of the element can remain fixed tothe substrate 107.

The intentionally grown dislocations of the present disclosure are incontrast to naturally occurring dislocations. Naturally occurringdisclosures are typically present, in approximately equal numbers, inboth substantially parallel (e.g., acute angles of less than about 45degrees) and substantially perpendicular directions (e.g., acute anglesof greater than 45 degree and less than or equal to 90 degrees) withrespect to each other. Moreover, the naturally occurring dislocationscan appear in random locations in a crystal. Randomly occurringdislocations can cause undesired distortions in the shape of crystalswhen the crystal is released from the substrate.

For some embodiments of the MEMS 102, such as shown in FIG. 1, thedislocations 110 are localized to one or more defect sub-regions 170 ofthe crystalline structural element 105. The location of the defectsub-regions 170 helps control where the released part 160 of the element105 bends. As illustrated in FIG. 1, the released part 160 of theelement 105 can bend out of the plane 140 of the substrate 107 with bentportions 172 of the structural element 105 occurring outside of thedefect sub-region 170. That is, the presence of a substantial density ofsubstantially parallel dislocations 110 relax stresses in the defectsub-regions 170 reduces the natural tendency of the sub-region 170 tobend when the element 105 is released from the substrate 107. Incontrast, the portions 172 of the structural element 105 occurringoutside of the defect sub-region 170 bend to release their stresses whenthe element 105 is released from the substrate 107. Although only twobent portions 172 are depicted in FIG. 1, the element 105 could have oneor a plurality of bends that are produced as a consequence of forming adifferent numbers of defect sub-regions 170.

The term defect sub-region 170, as used herein, refers to that portionof the crystalline structural element 105 having a substantiallyelevated density of dislocations 110. For instance, the density ofdislocations 110 in the defect sub-region 170 can be at least about 2times higher, and in some cases about 20 or more times higher, than inremaining regions of the element 105. One skilled in the art wouldunderstand how to quantify the density of the dislocations 110. Forinstance, the defect sub-region's 170 total volume, or area at theinterface 155, can be quantified by inspecting plan or cross-sectionalviews of TEM or CL images of the crystalline structural element 105. Thenumber of dislocations 110 within the defect sub-region 170 in thesesame TEM or CL images can be counted, and the density calculated. Misfitdislocation density can be quantified by counting the number ofdislocations that cross a line 173 perpendicular to the dislocation in adefect sub-region 170. For example, in some cases, the misfitdislocation density in some crystalline structural elements 105 canequal about 1×10⁵ cm⁻¹, or greater. One skilled in the art wouldunderstand how to similarly quantify the density of edge dislocations.

In other embodiments of the MEMS 102, the dislocations 110 can bedistributed throughout the crystalline structural element 105, or atleast, the releasable part 160 of the element 105. For example, thedensity of defects having said adjacent pairs dislocations with theabove described acute angle does not vary by more than 50% over thecrystalline structural element. The uniform distribution of dislocations110 can result in a substantially straight or planar element 105. Suchan embodiment is shown in FIG. 2, which presents a perspective view of asecond example apparatus 100 and MEMS 102 of the present disclosure. Thedislocations 110 (e.g., misfit dislocations) run substantially parallelto each other across the short axis 210 (e.g., substantiallyperpendicular to long axis 220) of the released part 160 of abeam-shaped structural element 105. The misfit dislocations 110 arelocated substantially at the interface 155 between the two crystallayers 150, 152.

Having unidirectional dislocations 110 throughout the element 105, suchas depicted in FIG. 2, can advantageously stiffen the element 105. Therelative stiffness of a crystalline structural element 105 can bemeasured by the comparing voltages needed, in the presence and absenceof the dislocations 110, to deflect a structural element 105, forexample, configured as a cantilever. The dislocations 110 that travelalong the short axis 210 can substantially relax strain along the shortaxis 210 of the element 105. Consequently, the released part 160 of theelement 105 does not bend out of the plane 140 of the substrate 107. Insome cases, the element 105 can be stiffer as compared to an identicalcrystalline structure element of substantially the same compositionwithout the unidirectional misfit dislocations running substantiallyparallel to the short axis 210.

In some cases, there may still be strain along the long axis 220 of thecrystalline structural element 105. One possible consequence of this isillustrated in FIG. 2. The release of part 160 of the element 105results in slight curling at the tip 230 of the element 105. In suchcases, the final shape of the released element 105 can have asubstantially planar major side 240 and a curved minor side 250 (seealso inset FIG. 2A, showing a plan view of a portion of the crystallinestructural element 105).

FIG. 3 presents a perspective view of a third example apparatus 100,having another embodiment of a portion of the MEMS 102. Similar to theembodiment depicted in FIG. 1, the crystalline structural element 105shown in FIG. 3 can have misfit dislocations 110 located at theinterface 155 between the first and second crystal layers 150, 152 ofthe element 105. The defect sub-region 170 having such dislocations 110remains substantially planar, while outside of the defect subregionsthere are bent portions 172. In this embodiment, however, the element105 also includes edge dislocations 310 located in the single crystallayer 150. As illustrated, the misfit dislocations 110 and edgedislocations 310 can be substantially parallel to the short axis 210 ofthe beam-shaped crystalline structural element 105.

Edge dislocation 310 formation can be facilitated by the misfitdislocations 110 originating from nucleation sites 130. For instance, insome embodiments, the single crystal layer 150 can have a crystalorientation that is slightly tilted off a <001> direction (e.g., tiltedby about 1 to 10 degrees). In such embodiments, at least some of themisfit dislocations 110 propagating from the nucleation sites 130 willtilt toward and, intersect with, each other. Some of these intersectingmisfit dislocations 110 interact with each other so as to form the edgedislocation 310 that can extend into the single crystal layer 150.

FIG. 4 presents a perspective view of a fourth example apparatus 100,having another embodiment of the MEMS 102. The crystalline structuralelement 105 in this embodiment, consists essentially of a single crystallayer 150, with edge dislocations 310 located in the single crystallayer 150. The edge dislocations run substantially traverse the width ofthe element 160. The embodiment in FIG. 4 is similar to the embodimentin FIG. 3 except that the second crystal layer 152 (FIG. 3) has beensubstantially entirely removed (e.g., greater than 99% removed) from thefinal MEMS 102. Consequently, the misfit dislocations 110 at theinterface 155 (FIG. 3) are removed, leaving only edge dislocations 110remaining within the element 105 (e.g., in the single or first crystallayer 150).

Analogous to the embodiment depicted in FIG. 3, the crystallinestructural element 105 shown in FIG. 4 still have a defect sub-region170, however the defects (edge dislocations 310) are in the singlecrystal layer 150. The crystalline structural element 105 can also havea bent portion 410. However, in contrast to the bent portions 172 forthe element 105 shown in FIG. 3, the bent portion 410 is located in thedefect sub-region 170 (e.g., the region with the edge dislocations).Moreover, portions of the element 105 outside of the defect sub-region170 retains their planar shape when released, because the stressesbetween the two layers 150, 152 are no longer present when the secondlayer 152 (FIG. 3) is removed. Additionally, the bend of the bentportion 410 is in the opposite direction to the bent portions 172 shownin FIG. 3 because the remaining edge dislocations 310 in the first layer150 are now the dominant stress producing feature in the layer 150.Consequently, to relieve such stress, the released element 105 bends atthe defect sub-region 170. For example, as illustrated in FIG. 4, a bendaxis 420 of the crystalline structural element 105 can be substantiallyparallel to the to an average direction (e.g., in the average directionof the direction vectors 115, FIG. 1) of the dislocations 310.

In other embodiments, the edge dislocations 310 can be distributedthroughout the single crystal layer 105, similar that shown in FIG. 2.In such configurations, the edge dislocations 310 in the single crystallayer 150, can curl upwards to relieve stresses throughout the element105, after releasing a part 160 of the element 105 from the substrate107.

Nucleation sites 130 can be present in the final crystalline structuralelements 105 shown in FIGS. 1, 2 and 3. In other embodiment, such asshown in FIG. 4, that portion of the crystalline structural elements 105having the nucleation sites 130 is removed. For example, referring toFIG. 3, a portion 320 of the crystalline structural element 105 havingthe nucleation sites 130 can be removed, before releasing the element105. FIG. 4 shows the resulting narrower short axis 210 nucleationsite-free crystalline structural element 105, after further removing thesecond crystal layer 152. Similar nucleation site-free crystallinestructural elements 105 could be prepared for the MEMS 102 presented inFIGS. 1 and 2.

Another aspect of the present disclosure is a method of manufacturing anapparatus. FIGS. 5-10B present perspective views of selected stages inan example method of manufacturing an apparatus 500. The method includesforming a MEMS 102 having a crystalline structural element 105. Any ofthe apparatuses discussed in the context of FIGS. 1-4 can be made by themethod. Any process steps already discussed in the context of FIGS. 1-4can be part of the method.

FIG. 5 shows the apparatus 500 after providing a substrate 107 having afirst crystal layer 150 located thereon. In some embodiments, thesubstrate 107 is a silicon-on-insulator substrate having a lower siliconlayer 510, silicon oxide layer 520 and upper silicon layer that is thefirst crystal layer 150.

FIG. 6 shows the apparatus 500 of FIG. 5 after patterning the firstcrystal layer 150 to form a blocking feature 135 of the first crystallayer 150. Any conventional patterning process, such as conventionalphotolithographic and dry etch procedures, can be used to form thelattice dislocation blocking feature 135. For the embodiment shown inFIG. 6, the first crystal layer 150 is patterned to have a base pad 610,arms 620 coupled to the base pad 610, and a cross bar 630 that couplesthe two arms together. As further illustrated in FIG. 6, there canremain portions 640 of the first crystal layer 150 that lay outside ofthe blocking feature 135.

FIG. 7 shows the apparatus 500 of FIG. 6 after forming one or morenucleation sites 130 in the blocking feature 135. For example, each ofthe nucleation sites 130 can be formed by implanting atoms (e.g.,germanium atoms) into the blocking feature 135 by conventionalprocesses. As shown in FIG. 7, the nucleation sites 130 can be locatedalong edges 710 of the blocking feature 135. Implanting atoms along theedges 710 can facilitate the subsequent removal of portions of theblocking features that contain the implanted atoms, if desired.

In some cases, a concentration of implanted atoms is substantially thesame in all of the nucleation sites 130. In other cases, there is aprogressive increasing concentration (e.g., a concentration gradient) ofimplanted atoms along a dimension of the blocking feature 135. Forinstance, as shown in FIG. 7, there is a row 720 of nucleation sites 130along the cross bar 630. The row 720 can have a plurality of equallyspaced nucleation sites 130. Each of nucleation sites 130 can havesubstantially the same concentration of implanted atoms. As also shownin FIG. 7, the arms 620 can each have a second row 730 with a pluralityof nucleation sites 130. The density of the nucleation sites 130 canprogressively increase along a dimension, for example the second rows730, towards the base pad 610. Alternatively, equally spaced nucleationsites 130 in the second rows 730 can have progressively increasingimplanted atom concentrations towards the base pad 610.

FIG. 8 shows the apparatus 500 of FIG. 7 after covering the firstcrystal layer 150 with a second crystal layer 152 (e.g., SiGe). Thesecond crystal layer 152 also can cover the blocking features 135 andits nucleation sites 130 (FIG. 7). Any conventional blanket or selectivedeposition process such as chemical vapor deposition (CVD) or physicalvapor deposition (PVD) can be used to deposit the second crystal layer152. For example, the deposition process (e.g., vapor phase epitaxy ormolecular beam epitaxy processes) may enable epitaxial growth of thesecond crystal layer 152.

As noted in the context of FIGS. 1-4, the compositions of the first andsecond layers 150, 152 are selected such that the first crystal layer150 and the second crystal layer 152 have different bulk latticeconstants (for example differing by at least about 0.1 percent).Consequently, misfit dislocations 110 form at the interface 155 betweenthe two strained crystal layers 150, 152. A majority (for example atleast about 60 percent) of the misfit dislocations 110 have directionvectors 115 (FIG. 1) that form an acute angle 120 (FIG. 1) angles ofless than about 45 degrees between adjacent pairs of the misfitdislocations 110. For example, for the embodiment shown in FIG. 8, themajority of the misfit dislocations 110 can be formed along a short axis210 of the arms 620 and the cross bar 630 of the crystalline structuralelement 105.

FIG. 9 shows the apparatus 500 of FIG. 8 after removing portions 640(FIG. 6) of the first crystal layer 150 that lay outside of the blockingfeature 130. Any of the conventional patterning process discussed in thecontext of FIG. 6 can be used to remove the portions 640 of the firstcrystal layer 150 that are not part of the blocking feature 135.

The same conventional patterning process may also be used to removeportion the second crystal layer 152 that lay over the outlying portions640 of the first crystal layer 150. In other embodiments, a separateconventional patterning process can be used to remove the overlyingsecond crystal layer 152. The conventional patterning process used toremove the outlying portions 640 can also be used to remove thenucleation sites 130 (FIG. 7) in the first crystal layer 150, and toremove the second crystal layer 152 that lay directly over thenucleation sites 130. In other embodiments, however, a separateconventional patterning process can be used to remove the nucleationsites 130. Sometimes it is desirable to remove the nucleation sites 130because portions of the crystal layer 150 in the vicinity the nucleationsites can be sufficiently damaged to break during mechanical or thermalstresses imposed on the MEMS 102. It can also be desirable to remove thenucleation sites 130 because portions the crystal layer 150 in thevicinity of the nucleation sites can be sufficiently damaged to modifythe stress distribution, and therefore, the final shape of the MEMS 102during handling or during its intended operation. In still other cases,however, the nucleation sites 130 are not removed.

FIG. 10A shows the apparatus 500 of FIG. 9 after removing at least partof an underlying layer of the substrate 107 (e.g., one or both of thelower silicon layer 510 and silicon oxide layer 520). Any conventionalprocess (e.g., a release etch comprising hydrofluoric acid) can be usedto release a portion of the crystalline structural element 105 from thesubstrate 107. For the embodiment shown in FIG. 10A, the crystallinestructural element 105 is released such that a first part 160 (e.g.,arms 610 and cross bar 630) of the blocking feature 135 is separatedfrom the substrate 107, while a second part 165 (e.g., base pad 610) ofthe blocking feature 135 remains fixed to the substrate 107. FIG. 10Ashows the first part 160 of the blocking feature 135 at a transitionalstage where the first part 160 has been released from the substrate 107,but the part 160 has not yet bent to relieve its stresses.

FIG. 10B shows the first part 160 of the blocking feature 135 afterbeing released from the substrate 107 and after bending. The first part160 has bent towards the first crystal layer 150, analogous to thatdepicted in FIG. 1. For the embodiment shown in FIG. 10B, the arms 620of the first part 160 have curled. Because of the progressive increasein the nucleation sites 130 (FIG. 7) towards the base pad 610, thereleased arms 620 curl down to form a structural element 105 with acoiled part 160. In other embodiments, the crystalline structuralelement 105 can be configured to bend towards the second crystal layer152 after being released. Such could be the case, for example, if thefirst crystal layer 150 is composed of silicon germanium and the secondcrystal layer 152 is composed of silicon or an alloy of silicon andgermanium with less germanium present than in the first layer.

One skilled in the art would understand how the example manufacturingprocesses presented in the context of FIGS. 5-10B could be adapted tomake any of the MEMS 102 shown in FIGS. 1-4. In some embodiments, forexample, the nucleation sites 130 can be located such that misfitdislocations 110 are formed throughout crystalline structural element105, similar to that shown in FIG. 2. Consequently, upon being released,the fully relaxed released part 150 of the crystalline structuralelement 105 can be a planar bi-crystalline layer, such as shown in FIG.2.

In other embodiments, conventional patterning processes are used toremove the overlying second crystal layer 152 (FIG. 9), includingremoving substantially all of the layer 152 laying directly above theraised portions 135. The second crystal layer 152 (FIG. 9) is removedafter the misfit dislocations 110 (FIG. 8) have induced the formation ofedge dislocations 310 (FIG. 3). This process can be used to formembodiments such as shown in FIG. 4, where edge dislocations 310 are inthe first crystal layer 110.

In some embodiments, patterning of the first crystal layer can furtherinclude forming a second blocking feature of the first crystal layer.This is illustrated in FIG. 11 for example apparatus 1100. FIG. 11 showsan alternative embodiment of the patterning step discussed above in thecontext of FIG. 6. In addition to patterning the first crystal layer 150to form the blocking feature 135 (e.g., a raised feature), a secondblocking feature 1105 is formed (e.g., a raised or lowered feature). Thesecond blocking feature 1105 can be located adjacent to the nucleationsite 130. FIG. 11 also shows the apparatus 1100 after forming anucleation site 130 in the first crystal layer 150.

FIG. 12 shows the apparatus 1100 of FIG. 11 after covering the firstcrystal layer 150 with a second crystal layer 152. Analogous to thatdiscussed in the context of FIG. 8, the second crystal layer 152 cancover the blocking feature 135 and second blocking feature 1105. Asfurther illustrated in FIG. 12, the second crystal layer 152 can beselectively patterned such that it only covers certain sections of theblocking feature 135. FIG. 12 illustrates that the second blockingfeature 1105 helps to guide the growth of dislocations 110 (e.g., misfitdislocations) in a particular direction. For instance, the secondblocking feature 1105 can limit dislocation growth in undesireddirections. As illustrated, the resulting misfit dislocations 110 can becontrolled to grow parallel to the short axis 210 of the first part 160of the element 105. The second blocking feature 1105 helps to preventthe excessive growth of misfit dislocations 110 in the fixed part 165 ofthe element 105. Of course, multiple first and second blocking features135, 1100 could be formed, if desired, to further control where misfitdislocations 110 are formed.

FIG. 13 shows the apparatus 1100 of FIG. 12 after removing portions ofthe first crystal layer 150 that lay outside of the blocking feature135, and the second blocking feature 1105, analogous to that presentedin FIG. 9. FIG. 13 also shows the apparatus 1100 of FIG. 12 afterreleasing the first part 160 of the element from the substrate 107,analogous to that presented in FIGS. 10A and 10B. As shown in FIG. 13,the released first part 160 rotates out of a plane 140 of the substrate107 around a bend axis 175 that is parallel to the direction vectors(FIG. 1) of the dislocations 110 (FIG. 12).

Although the embodiments have been described in detail, those ofordinary skill in the art should understand that they could make variouschanges, substitutions and alterations herein without departing from thescope of the disclosure.

1. A method of manufacturing a device, comprising: forming a microelectromechanical system having a crystalline structural layer, including: providing a substrate having a first crystal layer located thereon; patterning said first crystal layer to form a lattice dislocation blocking feature; forming one or more nucleation sites in said lattice dislocation blocking feature; and covering said first crystal layer with a second crystal layer, wherein: misfit dislocations form at an interface between said first crystal layer and said second crystal layer, and at least about 60 percent of adjacent pairs of said misfit dislocations have direction vectors of said adjacent pairs form acute angles of less than about 45 degrees.
 2. The method of claim 1, further including removing portions of said first crystal layer that lay outside of said lattice dislocation blocking feature, wherein said removing portions of said first crystal layer includes removing said one or more of said nucleation sites and portions of said second crystal layer lying directly above said nucleation sites.
 3. The method of claim 1, further including removing at least part of an underlying layer of said substrate such that a first part of said lattice dislocation blocking feature is released from said substrate and a second part of said lattice dislocation blocking feature remains fixed to said substrate, wherein said crystalline structural layer has a suspended portion, corresponding to said first part of said lattice dislocation blocking feature, whose major or minor surface is bent.
 4. The method of claim 3, wherein said suspended portion of said crystalline structural layer is bent away from said second crystal layer after said releasing.
 5. The method of claim 3, wherein said suspended portion of said crystalline structural layer is bent towards said second crystal layer after said releasing.
 6. The method of claim 1, wherein a concentration of implanted atoms is substantially the same in all of said nucleation sites.
 7. The method of claim 1, wherein said nucleation sites are located along an edge of said lattice dislocation blocking feature.
 8. The method of claim 1, wherein said nucleation sites progressively increase in said nucleation site density, or in implanted atom concentration, along a dimension of said lattice dislocation blocking feature.
 9. The method of claim 1, further including entirely removing said second crystal layer after forming said misfit dislocations such that edge dislocations remain in said first crystal layer.
 10. The method of claim 1, wherein said patterning of said first crystal layer includes forming a second lattice dislocation blocking feature of said first crystal layer, said second lattice dislocation blocking feature being located adjacent to said nucleation site.
 11. The method of claim 1, wherein said first crystal layer and said second crystal layer have bulk lattice constants that differ by at least about 0.1 percent. 